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<html lang="zh">
    <head>
        <meta charset="UTF-8" />
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        <meta name="viewport" content="width=device-width, initial-scale=1.0" />
        <title>Document</title>
        <script>

            //debugger // 在代码中打了一个断点

            console.log(a) // 2

            var a = 1

            console.log(a) // 1

            function a() {
                alert(2)
            }

            console.log(a) // 1

            var a = 3

            console.log(a) // 3

            var a = function () {
                alert(4)
            }

            console.log(a) // 4

            var a

            console.log(a) // 4
        </script>
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    <body></body>
</html>
